Prosthetic devices of various types have proven very useful in restoring function and mobility in patients. Many of such prosthetic devices are the type which are intended for implantation in the body, e.g., joints. In such circumstances it is necessary for the devices to be secured to bone structure in some manner.
Particular prosthetic devices which are useful as joints in the human body are described in U.S. Pat. No. 4,349,922, incorporated herein by reference. Although such devices are useful as joints in the wrist and hand, they are especially useful as joints between a metacarpal bone and a proximal phalanx (i.e., the metacarpophalangeal joint).
The prosthetic devices of the type just referred to include two portions which are pivotably and rotationally coupled together so as to enable relatively normal movement of the fingers of the hand after implantation. Each of the two portions of the prosthetic device includes an elongated stem member which is adapted to be inserted into and anchored within separate bone structure in the body, as described and taught in the aforementioned patent.
The prosthetic devices referred to above are especially useful in replacing the normal joint between the metacarpal bone and proximal phalanx of persons afflicted with severe arthritis, particularly rheumatoid arthritis in which there are advancing degrees of destruction of the articular joint surfaces associated with erosion of the bone and attenuation of the collateral ligaments with secondary subluxation or dislocation of the base of the proximal phalanx on the metacarpal head. In such cases it is often necessary to replace more than one, and often four, of the metacarpal phalangeal joints of the fingers in one operation because of the progression and extent of the disease.
For this type of surgery it is necessary to use a tourniquet to prevent blood loss while the prosthetic devices are being implanted. However, use of a tourniquet in this situation should typically be limited to no more than two hours in order to help avoid complications secondary to tissue ischemia. Therefore, it is advantageous to complete the implantation of the prosthetic devices within a two-hour period. Otherwise additional tourniquet times will be required. This, of course, requires extension of the anesthetic time, all of which relatively increases the risks to the patient.
Therefore, when there are multiple devices to be implanted in a given hand it is extremely desirable to have refined instrumentation which is able to facilitate the proper resection of arthritic bones at the appropriate angles to assure proper implantation of the prosthetic devices relative to the long axes of the bones with due respect for the angles of resection such that the installed metacarpophalangeal joints will allow flexion and extension of adjacent fingers to occur along parallel planes in space. This assures that the fingers will not be mal-rotated or cross over each other during flexion and extension.
In order to obtain the proper orientation of the prosthetic device with respect to the metacarpal bone, the head of the bone must be resected in a defined manner so that it is complementary to the apposed portion of the prosthetic device to be implanted in such bone. It is difficult to assuredly and reproducibly obtain the proper orientation of the prosthetic device(s) by simple visual observation.
There has not heretofore been provided instrumentation to assist in providing and controlling proper orientation of metacarpophalangeal joint prosthetic devices of the type described herein. Further, there have not previously been provided processes or techniques for efficiently and effectively assisting a surgeon in determining and obtaining proper resection of bone structure in which this type of prosthetic device is to be implanted.